Hesiod, Works and Days, 265

“The man who does evil against another harms himself.”

οἷ αὐτῷ κακὰ τεύχει ἀνὴρ ἄλλῳ κακὰ τεύχων,

Perhaps (Plato’s) Socrates was thinking of this when he said “doing wrong is worse than suffering it“.